Patrick Tansey

 Introduction: The long-bone fracture healing process requires a hematoma formation, callus formation, angiogenesis and remodeling of the bony-callus over years with osteoblast and osteoclast activity.¹ Bone regeneration should occur spontaneously after initial intervention, however up to 10% of all fractures fail to complete healing and are classified as non-union.² Non-unions cause persistent pain and functional impairment until subsequent treatment. The exact pathogenesis for non-union is unknown, but is predicted to be multifactorial.^2-3 Current treatment of non-union is autologous bone grafting, but this therapy is limited by pain at the donor site, and finite availability of graft material.^4-5 In search for improved patient care, the replicative and osteoblastic differentiation abilities of mesenchymal stem cells (MSC) present promising potential for non-union treatment. Studies show that adipose-derived stem cells are less invasive to acquire and significantly more available than their bone marrow counterparts, making them practical for use in applicative therapy.¹ Methods: Centrifugation and collagenase application of lipoaspirate produces a heterogenous stromal vascular fraction (SVF) pellet that contains a stem cell density 2,500-fold of bone marrow’s⁶. Among the heterogenous mixture are subpopulations of perivascular stem cells (PSCs), which have been shown to produce bone formation at a significantly higher rate than whole SVF.⁶ PSCs are isolated by selection of osteogenic cellular markers such as CD45-, CD90+, and CD105_low through magnetic-activated cellular sorting.^7-8 Enriched PSCs are loaded on to hydroxyapatite scaffolds and placed within bony defects in vivo and in vitro.^6-7 Alizerin and Alkaline Phosphatase staining assess osteogenic capability. Micro-CT is used to assess 3-D bone formation.^6-7 Results: CD90+ cells showed the greatest osteogenic potential. CD90 was found to express transiently during early stages of differentiation to help guide osteoblastic lineages.⁸ These findings, coupled with PSCs known osteogenic function without cultural expansion, emphasize the benefit of using subpopulations ready for immediate use.⁸ PSC histologic samples stained darker with Alizarin red, suggesting significant increase in calcification.⁶ Mouse models with PSC-seeded implants showed stronger mineralization than empty scaffold when analyzed for bone-volume and density with m-CT.⁷ Conclusions: The use of SVF cells in humans has not been well documented, but isolation procedures have been performed rapidly enough to make scaffold implantation parallel to surgery feasible.⁹ While adipose is an infinitely available resource, the cost of procedure must decline before treatment becomes practical.

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2. Calori, G, Albisetti W, Agusy A, Iori S, ‘Risk factors contributing to fracture non-unions’, 38: Injury 2007; S11 – S18
3. Hak, D, Fitzpatrick D, Bishop J, Marsh J, et al. ‘Delayed union and nonunions: Epidemiology, clinical issues, and financial aspects’ , 45 ( 2 ): Injury 2014; S3 – S7
4. Giannoudis, P, Gudipati S, Harwood P, Kanakaris N , ‘Long bone non-unions treated with the diamond concept: a case series of 64 patients’ , 46 ( 8 ): Injury 2015; S48 – S54
5. Flierl, M, et al. ‘Outcomes and Complication Rates of Different Bone Grafting Modalities in Long Bone Fracture Nonunions: A Retrospective Cohort Study in 182 Patients’ , 8 ( 33 ): Journal of Orthopaedic Surgery and Research 2013; Web.
6. James AW, Zara JN, Corselli M, et al. An Abundant Perivascular Source of Stem Cells for Bone Tissue Engineering. Stem Cells Translational Medicine. 2012;1(9):673-684. doi:10.5966/sctm.2012-0053.
7. König MA, Canepa DD, Cadosch D, et al. Direct transplantation of native pericytes from adipose tissue: A new perspective to stimulate healing in critical size bone defects. Cytotherapy. 2015;18(1):41-52. doi:10.1016/j.jcyt.2015.10.002
8. Chung MT, Liu C, Hyun JS, et al. CD90 (Thy-1)-Positive Selection Enhances Osteogenic Capacity of Human Adipose-Derived Stromal Cells. Tissue Engineering Part A. 2013;19(7-8):989-997. doi:10.1089/ten.tea.2012.0370.
9. Saxer F, Scherberich A, Todorov A, Studer P, Miot S, Schreiner S. Implantation of Stromal Vascular Fraction Progenitors at Bone Fracture Sites: From a Rat Model to a First-in-Man Study. Stem Cells. 2016;34(12):2956-2966. doi:DOI: 10.1002/stem.2478